The advent of central heating relegated the fireplace to a decorator's item. The relatively recent reality regarding the uncertainty as to the quantity and cost of fossil fuels has necessitated a rethinking as to how the fireplace might be employed as at least a supplemental heat source.
The heat emanating from the fireplace may warm those sitting in close proximity thereto, and its radiant energy may tend to warm the immediate room, but the operating fireplace induces an air flow which reduces the overall heating efficiency of the primary heat source. So long as the fireplace is operating there is an endless trail of warm, expensive household air racing up the chimney. For years no one objected. Energy to operate the central heating system was available in abundance, and at relatively low cost.
Gradually it became apparent that the world's fuel supplies did not issue forth from a cornucopia; rather, the supply was finite; some fuels, such as wood, could be replenished if its source were carefully husbanded, but overall the cost of fossil fuels continued to rise. By the early 1970's the crunch was widely felt.
Many people boarded up their fireplaces; some closed and sealed the dampers to their fireplaces; and, other judiciously operated their fireplaces only on those days when the resultant overall loss of heat would not be sorely felt. This created the paradox of not being able to use the fireplace on truly cold days.
It is estimated that there are currently in excess of twenty million masonry fireplaces in the United States, and with that available market the fireplace insert was developed. The fireplace insert converts the outmoded fireplace into a valuable secondary heat source and still permits man the luxury of fulfilling the primordial instinct of watching a crackling fire while basking in its cozy warmth.
Currently, manufacturers are providing fireplace inserts in a wide variety of models. Initially, a self-contained firebox was simply inserted into the old fireplace opening, and a shroud was fitted between the insert and the facing of the original fireplace opening to minimize the undesirable exiting air flow. However, this arrangement has two major drawbacks. Not only is an effective seal between the insert and the old fireplace opening virtually impossible to effect, but such an arrangement inherently exposes the exhaust gases to an excessive surface area which serves to cool the exhaust gases allowing them to condense and deposit creosote within the old fireplace as well as upwardly along the interior of the chimney. Creosote deposits are a natural fire hazard and must be avoided.
Both drawbacks can be greatly minimized by the use of a positive interconnect system that extends at least between the exhaust vent of the insert and the damper frame. Such positive interconnect systems have heretofore been employed, but they are rather difficult to install.
In addition, it may also be desirable to effect a direct, enclosed flow path from the damper to the flue liner in the chimney. A smoke chamber is normally provided between the damper and the flue of the chimney, and the use of an enclosed flow path therethrough can eliminate any tendency for creosote to be deposited on the walls of the smoke chamber. The enclosed flow path from the damper to the flue also tends to maintain a higher flue temperature which serves to increase the draft action of the chimney and results in a further improved performance of the insert.
Heretofore, a corrugated connector duct has been employed to effect the enclosed flow path from the damper to the flue, and while such an arrangement is very attractive when depicted on sales brochures, the actual installation requires that the duct be bent in an S-shaped curve during installation. Chimney dimensions and layouts are not standard, and that precludes pre-shaping the corrugated duct work. In fact, the majority of chimney layouts even prevent the duct from being shaped prior to insertion. As a result, the installer must attempt to bend the corrugated duct after it is partially inserted through the damper, and it must be appreciated that he is attempting to bend the portion already inserted. This is a difficult task, at best, and virtually impossible in some chimneys because of their interior configuration.